(a) Field of the Invention
A positive active material precursor for a rechargeable lithium battery and a preparation method thereof, and a positive active material and a rechargeable lithium battery including the same are disclosed.
(b) Description of the Related Art
As use of small portable electric/electronic devices has widely increased, a new rechargeable battery such as a nickel hydrogen battery or a rechargeable lithium battery has been actively developed. The rechargeable lithium battery uses carbon such as graphite and the like as a negative active material, a metal oxide including lithium as a positive active material, and a non-aqueous solvent as an electrolyte solution. The lithium is a metal having high ionization tendency and may realize a high voltage, and thus is used to develop a battery having high energy density.
The rechargeable lithium batteries mainly use a lithium transition metal oxide including lithium as a positive active material, and specifically, 90% or more use a layered lithium transition metal oxide such as cobalt-based and nickel-based lithium transition metal oxides, a three component-based lithium transition metal oxide in which cobalt, nickel, and manganese coexist, and the like.
However, the layered lithium transition metal oxide that is widely used as a conventional positive active material has reversible capacity of less than or equal to 200 mAh/g and thus has a limit in terms of energy density. Accordingly, in order to solve the problem of a rechargeable lithium battery due to the limited reversible capacity of a positive electrode, research on a lithium-rich layered oxide (OLO) excessively including lithium instead of the layered lithium transition metal oxide is being undertaken.
A positive active material including the lithium-rich layered oxide has a solid solution structure in which a Li2MnO3 phase is combined with the conventional layered lithium transition metal oxide, and may realize high capacity of greater than or equal to 200 mAh/g since oxygen is dissociated from the Li2MnO3, and lithium is extracted therefrom when initially charged at 4.6 V.
However, this positive active material including the lithium-rich layered oxide may not be sufficiently electrochemically activated due deteriorated particle density and non-uniform composition depending on depth when charged at a high voltage, since a uniform composition distribution is difficult to obtain during manufacture of a precursor of the positive active material. Accordingly, a battery including the lithium-rich layered metal oxide has a problem of decreased discharge capacity and aggravated manganese elution at a high temperature and a high voltage, and thus has deteriorated battery performance and cycle-life characteristics.
Therefore, attempts to increase the particle uniformity and density in the lithium-rich layered oxide have been continuously applied to improve discharge capacity and cycle-life characteristics of a battery. The present invention attempts to solve this problem and thus to improve rate capability and cycle-life characteristics of a rechargeable lithium battery by uniformly distributing transition metals inside the lithium-rich metal oxide particle.